The measurement of blood pressure is a common procedure used in hospitals, clinics and physicians' offices as a tool to assist in diagnosis of illness and monitoring of sick patients, as well as an indicator of the general status of a person's health. In standard non-invasive blood pressure measurement practice, blood pressure is measured using an inflatable sleeve, commonly referred to as a cuff, to measure arterial blood pressure. The cuff, which is adapted to fit around a limb over an artery of a patient, typically around the patient's arm over the brachial artery, includes an interior chamber adapted to be inflated with air to provide a certain amount of pressure on the artery in the arm.
Electronic blood pressure measurement devices for automatically inflating the cuff and automatically sensing the blood pressure either during inflation of the cuff or during deflation of the cuff are well-known in the art. In such devices, a motor driven pump is operatively connected to the interior chamber of the cuff by means of a tube, commonly referred to as a lumen. Upon activation of the pump motor, air is pumped by the pump through the tube to inflate the interior chamber of the cuff to a pressure sufficient pressure on the artery to stop the blood flow through the artery. A bleed valve is also operatively connected in fluid communication with the interior chamber to permit depressuring of the interior chamber when it is desired to deflate the cuff, either step-wise or rapidly, as desired. Generally, a pressure sensing device, typically a pressure transducer, is operatively connected in fluid communication with the interior chamber of the cuff to directly sense the pressure within the interior chamber of the cuff.
Automated blood pressure measurement devices commonly employ either an ausculatory technique or an oscillometric technique to detect when the systolic blood pressure, which corresponds to the cessation of blood flow through the artery, is reached, and when the diastolic blood pressures, which corresponds to unrestricted blood flow through the artery, is reached. In a conventional ausculatory method, a sound sensing device, commonly a microphone, is provided in operative association with the cuff to listen for pulsating sounds, known as Korotkoff sounds, associated with the flow of blood through an artery under pressure. In a conventional oscillometric approach, one or more pressure sensing devices, for example pressure transducers, are provided in operative association with the cuff to detect small oscillatory pressures that occur within the cuff as the result of the pulsating characteristic of blood flow through the artery.
Electronic circuitry, including a central processing unit, is provided that processes the signals from the sensors and determines the systolic and diastolic blood pressures. Typically, a digital display is also provided for displaying the systolic and diastolic blood pressures. Alternatively, the signals indicative of the systolic and diastolic blood pressure measurements may be transmitted to an external device, such as a laptop or a patient monitor, for display and/or data recording.
A detailed discussion and description of the operation of an exemplary embodiment of an electronic apparatus for the non-invasive measurement of blood pressure is presented in co-pending U.S. patent application Ser. No. 10/619,380, filed Jul. 14, 2003, subject to assignment to the common assignee of this application, and entitled “Motion Measurement In A Blood Pressure Measurement Device”, and published Feb. 10, 2005, as Patent Application Publication No. US2005/0033188A1, which application is incorporated herein by reference.
Pressure transducers are analog devices, that is, the output signal from a pressure transducer is an analog signal. To be processed by the central processing unit, the analog signal must first be converted to a digital signal. To this end, conventional electronic blood pressure measurement devices include an analog-to-digital converter that functions to convert the analog signal from the pressure transducer to a digital signal for further processing.
Although such conventional prior art automatic blood pressure monitoring devices are effective, components such as pressure transducers and analog-to-digital converters are costly and complicate the devices. The need exists for a lower cost automatic pressure measurement device having fewer components or lower cost components.